Search Results (572)

We propose a time-delay signature suppressed broadband chaotic (TSBC) carrier generation scheme and theoretically investigate its performance in a dual-polarization bidirectional chaotic communication system based on synchronized vertical-cavity surface-emitting lasers (VCSELs). The TSBC scheme is implemented by combining fiber Bragg grating (FBG) feedback with an external electro-optic (EO) phase modulation loop to introduce synergistic nonlinear perturbations. The results demonstrate that the proposed TSBC scheme effectively suppresses the time-delay signature (TDS) to less than 0.03 while significantly enhancing the chaotic carrier bandwidth to over 23 GHz for each polarization channel. Meanwhile, high-quality chaotic synchronization can be achieved with laser parameter mismatches of approximately 30%. Finally, an aggregated 46 Gbit/s dual-polarization bidirectional chaotic transmission is demonstrated, which confirms the effectiveness and the potential of the TSBC dual-polarization bidirectional scheme for secure optical communication applications. Full article

Wavelength stability of distributed feedback (DFB) semiconductor lasers in dense wavelength division multiplexing (DWDM) systems hinges on sub-millikelvin temperature regulation, a task complicated by the nonlinear, multi-node dynamics of the thermoelectric cooler (TEC) and the purely reactive nature of conventional proportional–integral–derivative (PID) control. We present a physics-informed neural network (PINN) built around a residual correction architecture for hybrid feedforward–feedback TEC temperature control. Rather than penalizing physics-residual violations in the loss function, the architecture wires a simplified one-node thermal model directly into the network graph as a frozen baseline. A trainable branch then learns only the residual mismatch. Temporal lag features are appended to the input so that the network can reconstruct unmeasured internal thermal states from the cold-side temperature history, which proves essential for overcoming the partial-observability bottleneck inherent in multi-node TEC packages. Ablation experiments on a high-fidelity three-node TEC simulator show that all model variants (PINN, physics-feature-augmented NN, and pure NN) exceed R² = 0.993 when trained on the full dataset, yet the PINN’s advantage becomes pronounced under data scarcity. At a 3% training budget, it reaches R² = 0.966 versus 0.930 for the pure NN, implying an approximately 5.4× reduction in the data needed to reach a given accuracy target. In closed-loop validation, the PINN+PID hybrid settles 60% faster than standalone PID. Tracking RMSE drops by 69%, and peak disturbance deviation falls by 74%, across step, multi-setpoint, and current-perturbation scenarios. All results reported here are obtained in simulations. Experimental validation on physical DFB-TEC hardware is left to future work. Full article

Surface-emitting distributed-feedback (SE-DFB) semiconductor lasers based on second-order gratings face a fundamental triple constraint: the spatial co-location of gain, grating feedback, and vertical radiation functions limits single-mode selectivity, surface extraction efficiency, and far-field beam quality simultaneously. We propose a quasi-parity-time (PT)-symmetric SE-DFB laser with separated gain and radiating-grating sections. In this design, the electrically injected gain section and the passive second-order grating section are placed in different regions along the cavity axis, thereby separating electrical injection from surface emission without epitaxial regrowth. Coupled-mode theory and two-dimensional finite-element simulations demonstrate that the resulting longitudinal non-Hermitian gain–loss asymmetry produces spatial-overlap-dependent threshold discrimination, enabling an isolated low-threshold lasing branch that remains separated from competing cavity modes over the investigated pump-parameter range. Under the HR–AR boundary condition, the proposed design achieves a threshold gain margin of $\mathsf{\Delta }g=12.4$${\mathrm{c}\mathrm{m}}^{-1}$, more than six times that of a conventional HR–AR DFB benchmark considered here, together with an upward surface extraction efficiency of 23.4% obtained from 2D FEM simulations. A simplified steady-state rate-equation estimate further suggests that the increased threshold margin can support strong side-mode suppression. The design imposes no regrowth requirement and is fully compatible with standard single-growth InP ridge-waveguide fabrication. Full article

One of the main technological challenges in plasma wakefield acceleration (PWFA) research and development is achieving stable and reproducible acceleration. In particular, for PWFA schemes based on particle-driven plasma wave excitation, beam stability and timing jitter are increasingly critical. In these configurations, magnetic or radio-frequency (RF) compression schemes are often used, and the beam time-of-arrival jitter at the end of the linear accelerator can be strongly correlated with the phase noise of RF accelerating structures operated off-crest. For this reason, since 2008, an RF phase fast-feedback system acting within each RF pulse has been successfully implemented at Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare (LNF-INFN) at the Sources for Plasma Accelerators and Radiation Compton with Laser And Beam (SPARC_LAB) facility, operating on both S-band ($2.856$ GHz) and C-band ($5.712$ GHz) klystrons. This paper presents the upgrade and optimization of the fast-feedback system for an S-band klystron powered by a pulse-forming network modulator. This technology introduces significantly higher intrinsic phase noise than, for instance, solid state-based modulators. It is therefore essential to minimize such phase fluctuations to keep the machine stability under control. Both the feedback hardware (electronic boards and RF circuitry) and the software (controller and user interface) have been upgraded. Tests performed at SPARC_LAB achieved a reduction in klystron-induced jitter of a factor of 30, reaching values below 15 fs rms on both power plants. Moreover, adding a remote control of the feedback loop enabled a straightforward optimization of the operating point, allowing the phase stability performance to be pushed close to its practical limits. A detailed analysis of RF phase noise measurements with the fast-feedback loop in operation is also presented. Full article

Dissolved gas analysis (DGA) is an essential technique for the fault diagnosis and condition monitoring of oil-immersed power transformers. Among various characteristic gases, acetylene (C₂H₂) is a key indicator of high-energy discharge and arc faults. In this work, a high-sensitivity dissolved acetylene detection system is developed based on clamp-type quartz-enhanced photoacoustic spectroscopy (QEPAS). A specially designed clamp-type quartz tuning fork (Clamp-type QTF) is employed as the acoustic transducer to improve acoustic coupling efficiency and optical alignment tolerance. Compared with conventional standard quartz tuning forks, the clamp-type structure exhibits enlarged acoustic interaction volume, lower damping loss, and higher signal collection capability. A near-infrared distributed feedback (DFB) laser operating at 1531.6 nm is used as the excitation source. The dissolved gas is extracted from transformer oil using a headspace degassing module and introduced into the QEPAS cell for real-time measurement. Experimental results showed that the developed system achieves a 1σ-based SNR-estimated detection limit of 17 ppb at a 50 s integration time, derived from the continuous measurement of 0.75 ppm C₂H₂, with excellent linearity in the concentration range from 100 ppm to 500 ppm. The measured concentration of dissolved acetylene in transformer oil is in good agreement with gas chromatography (GC), validating the effectiveness and practical applicability of the proposed system. Full article

Trends in Micro- and Nano-Lithography required for future development of large area applications ranging from high-packing-density electronics to solar cells are surveyed and outlined. Strategies to use direct laser writing to define etch masks over large areas by: (i) fixed beam moving stage and (ii) moving beam moving stage approaches are presented. The extension of planar 2D and stacked 2D (or 2.5D) fabrication methods into 3D micro- and nano-fabrication is discussed. One of the essential future characteristics of 3D nanolithography is real-time feedback capability. This can be realised via inherent 3D-capable holography, which bridges lithographic exposure control, wavefront sensing, and adaptive feedback, providing a pathway to stitch-free, large-area 3D patterning. The future of micro-fabrication is expected to evolve via highly specialised 3D architecture design and reduction in post-processing steps. Full article

We demonstrate a reconfigurable microwave frequency measurement (MFM) scheme based on the period-one (P1) dynamics of an optically injected semiconductor laser. Unlike conventional architectures relying on electrical frequency-sweeping, our approach utilizes the P1 oscillation to generate a wideband linear optical chirp. A spectral gating mechanism is introduced, where an optical bandpass filter creates a negative temporal marker by rejecting free-running component of distributed feedback laser (DFB), thereby eliminating the need for external synchronization or pilot tones. The measurement range is flexibly tunable by adjusting the injection parameters, enabling a measurement range from 10 to 48 GHz. Experimental results demonstrate a frequency resolution of 50 MHz with chirp rate of 1 GHz/μs and a root-mean-square (RMS) error below 15 MHz, confirming the validity of this all-optical, self-referenced frequency-to-time mapping technique. Full article

To address the recognition challenges caused by blurred state boundaries and the limitations of single monitoring modalities during aircraft skin laser paint stripping, this study proposes a multimodal data fusion method for state recognition based on laser-induced breakdown spectroscopy (LIBS) and surface imaging. By constructing a synchronous monitoring platform, a dataset covering five key physical states, namely topcoat (Tc), topcoat–primer transition (Tc-Pr), primer (Pr), primer–substrate transition (Pr-As), and substrate damage (As), was established. The proposed gated weighted multimodal fusion network (PGMF-Net) employs SE-ResNet1D to capture variations in elemental composition features from the spectra and integrates ResNet18 to extract changes in surface morphology from the images. The experimental results show that the proposed model outperforms the single-modal methods as well as the compared early-fusion and late-fusion methods, achieving a recognition accuracy of 94.12% on the test set and an average accuracy of 94.87% in stratified cross-validation. The bootstrap-based confidence interval analysis further verifies the stability of this method under the current dataset conditions. Further analysis indicates that the single-spectrum model has difficulty effectively distinguishing coating transition states because different transition states contain identical or highly similar characteristic peak information. The single-vision model, however, shows insufficient sensitivity to subtle substrate damage, whereas multimodal fusion enables complementary representation of material composition information and surface morphological information. Experimental validation under different power conditions further confirms that the model outputs are generally consistent with the macroscopic morphological evolution observed on the sample surface. This method compensates for the limitations of traditional single-source monitoring and provides a methodological foundation for online monitoring and state feedback during the laser paint stripping process. Full article

Heat transport properties of serpentine minerals are important to the thermal state of subduction zones, but available data contain systematic errors from contact losses, radiative gains, deformation with pressure (P), and/or modelling short-comings. Here, laser flash analysis (LFA) provides thermal diffusivity (D) within ±3% as a function of temperature (T) of perpendicularly oriented, nearly pure Mg₃Si₂O₅(OH)₄ polymorphs, Al-rich lizardite with minor brucite, three serpentinites, plus chrysotile and lizardite near Ni₃Si₂O₅(OH)₄. Visible spectra show that Fe is mostly ferric and Cr³⁺ occasionally occupies tetrahedral sites. The proposed coupled substitution of Al³⁺ + OH⁻ replacing Si⁴⁺ + O²⁻ accounts for extra OH⁻ peaks in infrared spectra. Rietveld refinements and infrared spectra reveal that serpentine dehydration in LFA runs begins near 800 K. Thermal conductivity (K) vs. T is calculated within ~±5% from D, available heat capacity data, and ambient density. For antigorite, D and K are strongly anisotropic whereas chrysotile has extreme differences, but lizardite is nearly isotropic. A thermodynamic identity provides ∂(lnK)/∂P = 11 ± 1% Gpa⁻¹ for soft serpentine, double that of hard olivine. Lizardite becomes more thermally conductive than olivine near the 1 bar decomposition temperature, which increases with P. Through feedback, and because released H₂O vapor carries heat upwards, P,T conditions in serpentinized slabs follow the decomposition phase boundary during subduction. Full article

This work presents a machine-vision–based measurement and control framework for laser wire directed energy deposition (LWDED) processes. A visible-light camera system is used to capture meltpool images, from which a novel vision algorithm extracts the wire–meltpool interface location. By utilizing a camera that is rigidly mounted to the deposition head, the vision algorithm provides a relative measurement of the distance between the nozzle tip and the workpiece, also referred to as wire stickout. A proportional-derivative (PD) control strategy is implemented using the measured stickout as feedback to adjust deposition feedrate. Results show that the control system successfully compensates for improper layer height increments, enabling thin-wall builds to consistently reach target geometry. Full article

Giant cantilevered tree-shaped steel structures are highly susceptible to cumulative deformation and geometric deviation during staged construction due to their complex spatial configuration, long cantilever characteristics, and nonlinear load transfer mechanisms. To address these challenges, this study investigates deformation monitoring and control of such structures based on 3D laser scanning, taking the “Tree of Life” project as a representative case. A high-precision full-field monitoring system is established to acquire multi-stage point cloud data throughout the construction process. The collected data are registered with the BIM model to quantify spatial deviations and track the deformation evolution of key structural components. Meanwhile, a staged preloading–unloading strategy is implemented to simulate operational loads, reconstruct load transfer paths, and regulate structural deformation during construction. Based on continuous field measurements, the deformation characteristics of different structural regions, including ring beams, rotating platforms, and trunk–branch systems, are systematically analyzed. The results indicate that the structure exhibits a pronounced global torsional deformation pattern. The displacement of ring beams ranges from 40.35 mm to 80.15 mm, while the maximum local displacement reaches 131.37 mm in geometrically complex regions, primarily attributed to the coupling effects of complex geometry, long cantilever action, stiffness discontinuity, and load concentration. Furthermore, deformation exhibits a progressive and stage-dependent accumulation pattern under sequential loading–unloading processes. The proposed monitoring and control approach achieves millimeter-level accuracy and enables effective feedback for construction adjustment and deviation mitigation. The integration of 3D laser scanning with staged load regulation provides a reliable technical framework for deformation monitoring and control of complex cantilevered steel structures. While the findings are based on a single complex project, further validation on additional cases is required to fully establish the general applicability of the proposed framework, although its integration of 3D monitoring, BIM registration, and staged load regulation suggests potential transferability to other large-scale cantilevered steel structures with similar geometric complexity. Full article

Vertical-cavity surface-emitting lasers (VCSELs) have emerged as essential light sources for atomic-precision measurement, quantum-secure communication, high-speed optical transmission, and laser coherent scanning detection, owing to their low power consumption, high-quality beam characteristics, and ease of two-dimensional integration. However, the fundamental limitation on linewidth narrowing in VCSELs arises from their inherently short resonator, resulting in a natural linewidth on the order of 50–100 MHz. This limitation prevents conventional VCSELs from meeting the stringent requirements of advanced applications, making the ultra-narrow linewidth a key focus in optoelectronics research. This review analyzes representative achievements and application scenarios of narrow-linewidth VCSELs, evaluates the merits and limitations of industrial-grade devices, and envisions future directions in next-generation optoelectronic systems. Distinct from existing reviews, it integrates key single-mode fabrication techniques, quantitative linewidth requirements across applications, silicon photonic integration, and scalable manufacturing trends, establishing a complete mechanism–technology–application–industry analytical framework. Full article

This work presents a novel high-speed random bit generation approach based on chaotic optical signals combined with a pseudo-random pulse amplitude modulation (PAM) sequence. Chaotic dynamics generated by a laser diode under optical feedback provide the physical entropy source. At the same time, the PAM signal is added as an amplitude-level transformation to enhance the statistical distribution of the digitized signal. Unlike conventional post-processing techniques such as least significant bit (LSB) extraction, which reduce the effective bit rate, the proposed method described in this article preserves the full 8-bit resolution of the analog-to-digital converter improving the distribution of amplitude levels. Experimental results show a significant improvement in compliance with the NIST SP 800-22 statistical test suite. The system operates at a sampling rate of 20 GSa/s, achieving a theoretical bit generation rate of 160 Gb/s. These results demonstrate that the proposed approach provides an alternative to conventional digital post-processing techniques while maintaining high throughput. Full article

Keloids and hypertrophic scars are fibroproliferative disorders of wound healing characterized by excessive extracellular matrix deposition, constant inflammation, and high recurrence rates despite appropriate management. Conventional therapies, including surgical excision, corticosteroid injections, laser therapy, and radiation, can provide temporary relief. However, treatment failure remains common, specifically in refractory keloids. Recent findings suggest these outcomes cannot be fully explained by technical or mechanical factors alone, and pathological scarring may reflect underlying immune and neuroimmune dysfunction. Current evidence shows prolonged activation of pro-inflammatory and pro-fibrotic cytokine pathways like IL-6, TNF-α, TGF-β, and IL-17 drives sustain fibroblast activation and disrupts normal wound healing and remodeling. Additionally, the skin functions as an integrated neuro-endocrine-immune organ, allowing bidirectional communication between cutaneous nerves, immune cells, and stromal tissue. Neurogenic inflammation is mediated by neuropeptides, mast cell activation, and stress-induced hypothalamic–pituitary–adrenal axis dysregulation, which further amplifies inflammation within scar tissue. Psychiatric comorbidities like depression, anxiety, and chronic psychological stress serve as a positive feedback mechanism and are increasingly recognized as biologically active contributors to immune dysregulation. This review highlights critical gaps in current management strategies and emphasizes the need for biologically informed, multidisciplinary approaches to improve long-term outcomes for keloid and hypertrophic scar management. Full article

In the fields of atomic physics, quantum sensing, and precision measurement, 852 nm lasers are essential for the resonant excitation and manipulation of the cesium (Cs) D₂ transition ($6S_{1/2}\to 6P_{3/2}$). While significant global progress has been made in developing 852 nm laser based on distributed feedback (DFB) lasers and external cavity diode lasers (ECDL), the burgeoning demand for portable and integrated quantum instruments imposes stringent requirements on miniaturization and long-term, maintenance-free operation. To address the challenge of mode competition in Faraday lasers, this work demonstrates a frequency-stabilized semiconductor laser based on an atomic frequency-selective architecture. By utilizing a customized Faraday Anomalous Dispersion Optical Filter (FADOF) for frequency selection, the laser wavelength automatically corresponds to the Cs 852 nm D₂ transition, offering “Plug-and-play” operation. To further enhance integration, we propose and demonstrate a miniaturized Faraday laser architecture that resolves the instability caused by the mismatch between the FADOF transmission bandwidth and the free spectral range (FSR) of the external cavity. By employing a 7000 Gs magnetic field, the FADOF bandwidth is actively broadened to ∼15 GHz, while the cavity length is concurrently compressed to 30 mm to maximize FSR to effectively suppressing unstable mode competition. The resulting laser achieves a highly compact dimension of $102\times 109\times 96{\mathrm{mm}}^3$. Performance testing demonstrates a Lorentzian fitted linewidth of $16.4\mathrm{kHz}$ and a 1-s frequency stability of $3.05\times {10}^{-13}$ after modulation transfer spectroscopy (MTS)-based frequency locking. This robust and autonomous 852 nm laser source provides a critical technological foundation for the miniaturization of high-performance quantum sensors. Full article